1. Field of Invention
This invention relates the construction of a valve for hydraulic fluid leak detection and correction in hydraulic fluid linkages, insuring that the hydraulic fluid linkages are accurate at all times. The reliable accurate hydraulic fluid linkages with adjustable limit stops can be used to replace complex mechanical linkages.
2. Description of Prior Art
Hydraulic circuits have not been able to fully replace mechanical linkages in precision applications, such as vehicle steering and other systems requiring accurate reliable correlation which linkages provided. Mechanical linkages reliably correlate the movement of mechanical components. Hydraulic circuits used to replace mechanical linkages use two or more linear actuators, rotary actuators or fluid motors to control the movement of mechanical components. In a hydraulic circuit these hydraulic actuators or motors are connected by a hydraulic fluid conduit with possible intermediary fluid control valves and fluid pumps. The hydraulic circuits used to replace mechanical linkages are hydraulic linkages. Replacing mechanical linkages with hydraulic linkages have significant advantages over mechanical linkages. Hydraulic conduits required to construct hydraulic linkages can be easily routed. Hydraulic circuits can easily switch operating modes. In each operation mode the hydraulic circuit can form a hydraulic linkage between a different set of mechanical components or the mechanical components can be controlled independently in a completely uncorrelated manner. To replace mechanical linkages, hydraulic circuits need to be able to detect and correct fluid loss in hydraulic linkages and require limit stops to prevent damage caused by extending or retracing too far and/or too hard. Through the use of limit sensors and fluid limit valves, the hydraulic linkage can include leakage compensation and leakage location detection and allow for accurate control over the extension and retraction of a piston in the fluid actuator. Mechanical stops prevent over extension and over retraction and are strong enough to resist the full force of the hydraulic actuator or the full force of the mechanical load. Conventional actuators include mechanical stops. However, the mechanical stops included in conventional actuators are not adjustable. Mechanical components in different orientations may require mechanical limit stops to be repositioned. Without adjustable mechanical actuator stops, actuator movement often cannot be stopped before damaging over extension or over retraction occurs.
Piston bypass valves have been constructed to activate the piston when it is in proximity to the end cap. For example, see U.S. Pat. Nos. 5,425,305, 6,170,383 (Mauritz). The described art does not provide location adjustable piston bypass valves.
Re-phasing hydraulic circuits have been constructed of re-phasing cylinders utilizing fluid bypass ports. For example, see U.S. Pat. No. 4,463,563 (Krehbiel). The described art does not provide location adjustable piston bypass valves. Also, neither the location nor the pressure at which these pistons are re-phased, by means of a bypass port, is adjustable.
Hydraulic steering linkages have been constructed from a pair of hydraulically linked hydraulic cylinders. For example see U.S. Pat. Nos. 6,179,315 (Boriack) 3,212,793 (Pietrotroia). There is no means of detecting or correcting for hydraulic fluid leakage from the hydraulic linkage described in this prior art. Hydraulic leakage occurs in virtually all hydraulic circuits. Leakage can occur as hydraulic fluid lost from the hydraulic circuit, or as hydraulic fluid leaking across actuator seals.
Cushioning devices are constructed for decelerating and stopping pistons by restricting fluid flow. For example, see U.S. Pat. Nos. 4,397,218 (Spring), 6,557,456 (Norton). The presented cushioning devices do not include a means of adjusting the extension and/or retraction limits at which the cushioning limit valves are activated or proportionally activating the cushioning limit valves.
A limit switch with a sensing element is actuated when the operating actuator reaches an end position. The switching element stops the supply of hydraulic fluid to the operating actuator in response to the actuated sensing element. For example see U.S. Pat. Nos. 3,920,217 (Danfoss) and 3,941,033 (Danfoss). Proximity switches are used to detect the proximity of components before they come into contact. When proximity switches detect the limit position, valves are controlled to interrupt hydraulic supply to actuators preventing them from over extending or retracting. For example U.S. Pat. No. 4,165,674 (Weight). Rather than stopping or interrupting the hydraulic supply to actuators, the hydraulic flow can also be reduced, slowing the actuators' movement as it approaches the limit. A limit valve which controls the driving hydraulic flow by reducing the hydraulic pump stroke when the limit valve is moved to a predetermined limit is able to reduce the hydraulic flow as desired. For example see U.S. Pat. No. 5,117,935 (Hall). However, the limit sensors and valves designed to stop or reduce hydraulic supply to actuators cannot detect or correct hydraulic leakage in circuits. Separate mechanical stops are required to prevent mechanical loads from over extending or retracting the actuators.
Leakage in hydraulic linkages can be compensated by continuously monitoring the position by a sensor on the control element and by a sensor on the driven element. The hydraulic flow to the actuators is continuously adjusted according to the monitored positions of the control and driven element. For example U.S. Pat. No. 7,028,469 (Porskrog). Here the elements are linked by an electronic control system. This electronic monitoring system requires an electrical power supply at all times for the position sensors and the control valve solenoids. The electronic monitoring systems is only able to compensate for slow hydraulic leaks. The present invention is able to compensate for slow hydraulic leaks without requiring continuous monitoring of either the control or driven elements. The prior art method of compensating for hydraulic leaks by continuously monitoring the control and driven elements does not include adjustable mechanical stops required to prevent mechanical loads from over extending or retracting the actuators. Whereas the present invention does include adjustable mechanical stops.